The present invention relates to an initializing drive apparatus, particularly to an initializing drive apparatus for resetting an out-of-phase state of a stepping motor.
Conventionally, as a vehicular indicating apparatus using a stepping motor, an indicator instrument as shown by FIG. 1 is known. In the drawing, the indicator instrument includes a stepping motor 1, an indicator 2 moved in cooperation with rotation of the stepping motor 1 and a drive apparatus 4 for the stepping motor which regularly and reversely rotates the stepping motor 1. The above-described stepping motor 1 includes two excitation coils 1a1 and 1a2, a rotor 1b in which N and S poles are alternately magnetized by respective three poles and rotated in response to changes in excited states of the excitation coils 1a1 and 1a2 and gears id for transmitting drive force of the rotor 1b to the indicator 2.
The stepping motor 1 includes a piece 1e as a driven member provided on a rear side of the gear 1d on which the indicator 2 is provided and which is moved in cooperation with rotational movement of the rotor 1b, and a stopper 1f for mechanically stopping rotation of the rotor 1b by being brought into contact with the piece 1e which is provided at a containing case, not illustrated, the containing case contains the excitation coils 1a1 and 1a2, the rotor 1b, the gears 1d and the piece 1e. 
Rotation of the stepping motor 1 to direct the piece 1e to the stopper 1f is defined as reverse rotation. A rotational direction of the indicator 2 rotating reversely is defined as a reverse rotational direction Y4. In contrast thereto, rotation of the stepping motor 1 to separate the piece 1e from the stopper 1f is defined as regular rotation. A rotational direction of the indicator 2 rotating regularly is defined as regular rotational direction Y3. The stopper 1f is provided to indicate a graduation of, for example, 0 km/h on a dial when the stopper 1f is brought into contact with the piece 1e. 
Here, an explanation will be given of the principle of operating to rotate the stepping motor 1 in reference to FIG. 7 showing an example of a relationship between excited states of the excitation coils 1a1 and 1a2 and rotation of the rotor 1b as follows. First, when the stepping motor 1 is controlled to bring about an excited state determined in excitation step (1), that is, such that a side of the excitation coil 1a1 becomes S pole and b side of the excitation coil 1a2 becomes nonexcited, N pole of the rotor 1b is attracted to the a side of the excitation coil 1a1 and stabilized.
Next, when the operation proceeds to excitation step (2) and the stepping motor 1 is controlled such that the a side of the excitation coil 1a1 becomes S pole and the b side of the excitation coil 1a2 becomes S pole and magnetic forces of the two excitation coils 1a1 and 1a2 become equal to each other, the rotor 1b is stopped at a position rotated from a position of the rotor 1b of excitation step (1) by 15 degrees in an arrow mark Y2 direction. In accordance with rotation of the rotor 1b in the arrow mark Y2 direction, the indicator 2 is rotated in the arrow mark Y4 direction (refer to FIG. 1).
In the following, when the stepping motor 1 is controlled such that the a side of the excitation coil 1a1 and the b side of the excitation coil 1a2 respectively become nonexcited, S pole (excitation step (3))xe2x86x92N pole, S pole (excitation step (4))xe2x86x92N pole, nonexcited (excitation step (5))xe2x86x92N pole, N pole (excitation step (6))xe2x86x92nonexcited, N pole (excitation step (7))xe2x86x92S pole, N pole (excitation step (8)), the rotor 1b is rotated by respective 15 degrees in the arrow mark Y2 direction by following the change in the excited state. Further, in the excitation steps (2), (4), (6) and (8) in which both of the exciting coils 1a1 and 1a2 are magnetized, the stepping motor 1 is controlled such that the magnetic forces of the two excitation coils 1a1 and 1a2 become equal to each other.
When the stepping motor 1 is controlled to the excited state prescribed at excitation step (1) again from the excitation step (8), the rotor 1b is rotated by 15 degrees further in the arrow mark Y2 direction and stabilized. Therefore, by controlling the excited states of the excitation coils 1a1 and 1a2 by repeating a plurality of excitation steps (1) through (8) which differ from each other in accordance with a regular excitation pattern constituted by aligning excitation steps in a previously determined order (1)xe2x86x92(2) . . . xe2x86x92(8), the rotor 1b is rotated by respective 15 degrees in the arrow mark Y2 direction at respective steps. Hereinafter, notation of the rotor 1b in the arrow mark Y2 direction is referred to as reverse rotation.
In order to rotate the rotor 1b in the arrow mark Y1 direction, the excited states of the excitation coils 1a1 and 1a2 may be controlled in accordance with a reverse excitation pattern in which excitation steps constituting the regular excitation pattern are aligned in a reverse order such as excitation steps (8)xe2x86x92(7)xe2x86x92 . . . xe2x86x92(1). In accordance with rotation of the rotor 1b in the arrow mark Y1 direction, the indicator 2 is moved in the arrow mark Y3 direction (refer to FIG. 1). Hereinafter, rotation of the rotor 1b in the arrow mark Y1 direction is referred to as regular rotation.
Further, in order to change the excited states of the excitation coils 1a1 and 1a2 such as excitation steps (8)xe2x86x92. . . xe2x86x92(1), the drive apparatus 4 respectively inputs excitation pulses as shown by FIG. 8 to the a and b sides of the excitation coils 1a1 and 1a2.
Next, an explanation will be given of operation when the indicating apparatus is used in, for example, a vehicle speed meter as follows. The drive apparatus 4 is supplied with angle data D1 indicating a rotational angle of the rotor 1b in correspondence with a moving amount xcex8-xcex8xe2x80x2 which is a difference between a target position xcex8 which is an indicating position of the indicator 2 calculated based on vehicle speed information measured by a vehicle speed meter and a current position xcex8xe2x80x2. By controlling the excited states of the excitation coils 1a1 and 1a2 in accordance with the angle data D1 by the drive apparatus 4, the indicator 2 is moved by the moving amount xcex8-xcex8xe2x80x2 and indicates the target position xcex8.
Meanwhile, there is a case in which the indicating apparatus becomes out of phase in which the moving amount xcex8-xcex8xe2x80x2 of the indicator 2 to be moved inherently and an actual moving amount differ from each other owing to input of the angle data D1 superposed with vibration or noise of the vehicle. Further, when the out-of-phase is repeated, there is brought about a difference between the speed indicated by the indicator 2 and the speed information measured by the speed sensor and the indicating apparatus cannot indicate accurately.
Hence, in order to resolve such a problem, the drive apparatus 4 is made to carry out initializing operation, mentioned later. In the initializing operation, the drive apparatus 4 rotates the stepping motor 1 reversely such that the piece 1e is directed to move to the side of the stopper 1f at each time of making an ignition switch ON. When the piece 1e is brought into contact with the stopper 1f and the indicator 2 is mechanically stopped at a contact position which is at graduation of 0 km/h on the dial, the drive apparatus 4 holds the excitation coils 1a1 and 1a2 in a previously determined initial excited state and electrically stops rotation of the stepping motor 1. By carrying out the above-described initializing operation, there is carried out resetting operation for resetting the difference between the speed indicated by the indicator 2 and the speed information measured by the speed sensor.
However, it is necessary for the above-described indicating apparatus to rotate the rotor 1b such that the indicator 2 is moved by an angle (A+xcex1) which is larger than a pivoting angle A of the indicator 2 in order to firmly bring the piece 1e into contact with the stopper 1f. Therefore, there poses a problem that a time period for necessarily moving the indicator 2 by the angle (A+xcex1) is consumed in the resetting operation regardless of whether the difference is brought about between the speed indicated by the indicator 2 and the speed information measured by the speed sensoror regardless of whether the difference is large or small and time is excessively taken in the resetting operation.
Although the piece 1e is brought into contact with and stopped by the stopper 1f, rotation of the excitation coils 1a1 and 1a2 is not electrically stopped and therefore, the piece 1e repeats to be brought into contact with and separated from the stopper 1af, sound of xe2x80x9cclick, clickxe2x80x9d is emitted at every time of bringing the piece 1e into contact with the stopper 1f and the sound is unpleasant for a driver.
Hence, in order to resolve the above-described problem, there is known an indicating apparatus in which control of rotation of the rotor 1b is stopped to thereby finish the resetting operation simultaneously with bringing the piece 1e into contact with the stopper 1f. That is, during a time period in which the piece 1e is not brought into contact with the stopper 1f and the rotor 1b is rotating, induced voltage is generated at the excitation coil 1a1 or 1a2 controlled in the nonexcited state. Meanwhile, when the piece 1e is brought into contact with the stopper 1f and rotation of the rotor 1b is stopped, induced voltage is not generated in the excitation coil 1a1 or 1a2 controlled in the nonexcited state.
Attention is paid to the above-described, a detecting and excitation step is constituted by excitation step (1), (2), (5) or (7) at which either of the excitation coils 1a1 and 1a2 is controlled in the nonexcited state and at every time of controlling the excitation coils 1a1 and 1a2 by the detecting and excitation step, voltage across both ends of the excitation coil 1a1 or 1a2 which is brought into the nonexcited state can be detected.
The indicator 2 is integrated to the rotor 1b such that the indicator 2 is brought into contact with the stopper 1f in an excitation step one step preceding the detecting and excitation step in rotating reversely. Specifically, when the detecting and excitation step is constituted by excitation step (1), the indicator 2 is made to be brought into contact with the stopper 1f at the excitation step (2) which is an excitation step one step preceding the excitation step {circle around (1)} in rotating reversely.
When detected voltage across both ends of the excitation coil 1a1 or 1a2 exceeds a previously determined threshold, induced voltage is generated at the excitation coil 1a1 or 1a2 and it is determined that the rotor 1b is rotating. Meanwhile, there is conceived a constitution in which when the voltage across the both ends is equal to or smaller than the threshold, induced voltage is not generated, the piece 1e is determined to be brought into contact with the stopper 1f and stopped at a zero position and control of the excited state for rotating the indicator 2 reversely is stopped to thereby finish the resetting operation.
Meanwhile, according to the method of constituting the detecting and excitation step by the excitation step controlled in the nonexcited state as described above, the contact can be detected only at the excitation step (1), (3), (5) or (7) which is a half of the eight excitation steps (1) through (8).
Therefore, there is a case in which rotation of the rotor 1b is not stopped at the detecting and excitation step (1), (3), (5) or (7) and rotation of the rotor 1b is stopped at the excitation step (2), (4), (6) or (8) owing to a backlash of the gear 1d or the like.
Hence, conventionally, there has been a request of detecting the. contact at an arbitrary point. However, as shown in FIG. 8, at the excitation steps (2), (4), (6) or (8) the excitation coils 1a1 and 1a2 are excited by an excitation pulse having a duty ratio of 1. Therefore, in order to detect the contact at all of the excitation steps (1) through (8), there is only a method of providing a detecting coil separately from the excitation coils 1a1 through 1a2 which poses a problem in view of cost.
Hence, it is a problem of the invention to provide an initializing drive apparatus capable of firmly detecting that a driven member is brought into contact with a stopper by paying attention to the above-described problem.
In order to solve the aforesaid object, the invention is characterized by having the following arrangement.
(1) A initializing drive apparatus comprising:
an initializing driving unit for rotating a stepping motor including two of excitation coils so that a driven member moved in cooperation with an operation of rotating the stepping motor is moved toward a stopper for mechanically stopping rotation of the stepping motor by being brought into contact with the driven member;
a contact detecting unit for detecting that the rotation of the stepping motor is mechanically stopped by bringing the driven member into contact with the stopper; and
a drive stopping unit for electrically stopping the operation of rotating the stepping motor in accordance with the detection of the contact detecting unit,
wherein the initializing driving unit rotates the stepping motor by a predetermined angle at each time of changing excited states of the excitation coils in accordance with an excitation pattern constituted by aligning a plurality of difference excitation steps in a previously determined order for determining the excited states of two of the excitation coils,
wherein when the excited states of the excitation coils are controlled so that both of the two excitation coils are magnetized, the initializing driving unit inputs excitation pulses having a duty ratio less than 1 to the excitation coils, and
wherein the contact detecting unit detects the contact between the driven member and the stopper based on voltage generated in the excitation coils when the both of the two excitation coils are magnetized and the excitation pulses are not inputted.
(2) The initializing drive apparatus according to (1), wherein the contact detecting unit detects the contact between the driven member and the stopper based on the voltages generated in the two excitation coils when the excitation pulses are not inputted to the two excitation coils.
(3) The initializing drive apparatus according to (1), wherein the contact detecting unit detects the voltages generated in the excitation coils a plural number of times and detects the contact between the driven member and the stopper based on a result of the detection.